This invention relates to improvements to conventional methods and apparatuses for installing replacement pipe or otherwise inserting a pipe liner composition in an existing conduit, typically in place underground, using a normally rigid thermoplastic composition as the replacement pipe or pipe liner, and more specifically to modified PVC in a collapsed, folded, flexible condition as replacement pipe or pipe liner.
Folded and collapsed thermosetting plastic replacement pipeline or conduit material is known. For example, U.S. Pat. No. 5,447,665, the entirety of which is incorporated herein by reference, describes such a product which can be installed in existing underground conduit such as sewer pipe. In this reference, a thermoplastic material, such as PVC, is extruded and cooled to a folded and flattened shape which retains a folded memory when reheated thereby facilitating spooling for storage and use and later insertion in an underground conduit. See also, U.S. Pat. No. 5,397,513, which is incorporated herein by reference, and which describes folded normally rigid thermoplastic tubular membrane which can be inserted into an underground conduit to be repaired and inflated. See also, for example, U.S. Pat. Nos. 5,403,120; 5,368,809; 5,244,624, and 5,034,180, all of which are incorporated herein by reference.
After installation, reforming and cooling, however, many rigid thermoplastic pipe/conduit liner materials, especially rigid PVC, become susceptible to cold-stress cracking most commonly around service connection orifices. An important need therefor exists for an improved thermoplastic material which is suitable for use as a folded and flattened pipe/conduit liner material and which is resistant to cold stress cracking after installation.
Further, it is also desirable to provide a thermoplastic liner material which retains softness in its folded position long enough such that it can be installed with less time restrictions than conventional material.